This invention relates to electrical conduit junction boxes and means for securing the end of electrical conduit in such boxes. It is common to use electrical conduit to contain electrical wires for safety within walls or floors during construction of a building. Indeed, it part of building code requirements in many places to use such conduit. In the case of conduit that is to be buried in concrete floors, it is usual to use plastic electrical conduit consisting of a tube having rings of thicker diameter around the tube at closely spaced regular intervals. The narrower diameter grooves allow for increased flexibility while the thicker plastic in the rings provides additional strength. The rings are typically formed such that the walls of the rings abut the tube at a ninety degree angle. This allows an external gripping ring that can somehow be fitted around the tube in a groove formed by such walls to grip the ring and restrain against longitudinal pulling forces exerted on the electrical conduit.
Mechanisms that have been used previously to secure electrical conduit to a junction box have included having a flexible flange built into an aperture in the junction box, or having a like arrangement on a separate conduit end attachment that is then attached by threaded end and nut means in an aperture on the junction box.
Difficulties with such attachment mechanisms have occurred due to the significant pulling forces that can be applied to the conduit when heavy concrete is poured or other forces during construction are exerted on the conduit. The flexible flanges can fail by popping away from the conduit. If the flanges fail and the conduit pops out of the box, it can place stress on the electrical wire inside the junction box and can break the connection. Also, in the case of cement pours around the box, cement can enter the junction box and adversely affect the electrical connections within the box. In the case of the thread and nut conduit end piece, extra labor is involved in attaching the piece to the junction box.
The invention provides a generally cylindrical self-securing insert that operates by fitting into one of a plurality of tubular projections on the junction box. The self-securing insert is slightly longer than the tubular projection and has a diameter sized to slidably fit within the tubular projection. An outer flanged rim on one end of the self-securing insert prevents it sliding further into the tubular projection. A split flanged rim on the other end of the self-securing insert allows the other end to flex together to allow insertion of the self-securing insert into the tubular projection. An inner split rim adjacent to the split flanged rim operates in conjunction with a disposable end plug having a conical face that allows insertion of a corrugated electrical conduit to flex apart the split flanged rim when it protrudes from an inner end of the tubular projection. The inner split rim snaps into a groove between raised rings of the corrugated electrical conduit and secures it against withdrawal by a pulling force. Any such pulling causes the insert to move with its split flanged rim against the inner end of the tubular projection such that the inner split rim will not release the end of the corrugated electrical conduit. The self-securing insert can be made of a tough resilient plastic to enable it to flex for insertion of the corrugated electrical conduit and yet be strong enough to retain the corrugated electrical conduit upon substantial pulling force being exerted on the electrical conduit.
The self-securing insert can be used with pre-existing electrical junction boxes having tubular projections. Such boxes often have a pop-out plate in their tubular projections to keep cement and other construction debris from passing into the box through those projections that are unused and unfilled by a length of electrical conduit. A like pop-out disposable end plug can be used for the self-securing insert itself, the plug having a conical face that assists in pushing the plug and thence the electrical conduit end past the outwardly flexing inside split rim of the self-securing insert.
One preferred embodiment of the invention would be a self-securing insert system for electrical conduit junctions, comprising:
a) a generally cylindrical portion slightly longer than a tubular projection of an electrical conduit junction box into which tubular projection the self-securing insert is to be used;
b) an outer flanged rim on one end of the self-securing insert to prevent it from sliding through the tubular projection;
c) an opposite end of the self-securing insert having a plurality of end portions separated by splits aligned with the length of the cylinder, to allow the end portions to flex together for insertion of the self-securing insert into the tubular projection;
d) a plurality of split flanged outer rim portions extending from the end portions to prevent the self-securing insert from being pulled out of the tubular projection without flexing the end portions together;
e) a plurality of inner split rim portions on the end portions, the inner split rim portions being sized to fit between corrugation rings on a length of electrical conduit;
f) the end portions being made of a tough, resilient plastic material to enable flexing inward for insertion of the self-securing insert into the tubular projection, and to enable flexing outward for insertion into the self-securing insert of an end of a length of electrical conduit having corrugation rings;
g) the self-securing insert being supplied with a pop-out disposable end plug having a conical face for spreading out the end portions upon a length of electrical conduit pushing the pop-out disposable end plug through the self-securing insert;
h) an electrical junction box with a multiplicity of tubular projections sized to slidably receive the self-securing insert;
c) a plurality of such self-securing inserts are inserted into respective tubular projections on the electrical junction box, such that each outer flanged rim is adjacent to an outer end of each tubular projection, and each split flanged rim portion is adjacent to an area where an inner portion of a tubular projection is joined to the electrical junction box;
d) at least four end portions separated by splits aligned with the length of the cylinder, to allow the end portions to flex together for insertion of the self-securing insert into the tubular projection, and to reflex when released back into an unflexed state, and
e) each end portion having a split flanged outer rim portion to prevent the end portions from being pulled back out of the tubular projection; and an inner flanged rim portion to grip between corrugated rings of a length of conduit.
There exist electrical conduits of different diameters. The self-securing insert system accommodates the junction of a variety of such conduit, by having in a preferred embodiment an electrical junction box having a multiplicity of tubular projections of various sizes to slidably receive a multiplicity of like self-securing inserts of various sizes respectively, the tubular projections and the self-securing inserts being thereby adapted to receive and secure a multiplicity of electrical conduits having various diameters.